Nonlinear resistor and nonlinear resistor composition

ABSTRACT

A RESISTOR COMPOSITION HAVING A NONLINEAR VOLTAGE CHARACTERISTIC CONSISTING ESSENTIALLY OF ZINC OXIDE AND, AS AN ADDITIVE BISMUTH FLUORIDE, AND A NONLINEAR RESISTOR MADE FROM SAID COMPOSITION. THE RESISTOR COMPOSITION AND THE RESISTOR HAVE THE ELECTRICAL PROPERTIES THEREOF FURTHER IMPROVED BY THE ADDITION OF AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF COBALT FLUORIDE, MANGANESE FLUORIDE, STANNOUS FLUORIDE, NICKEL FLUORIDE, CHROMIUM FLUORIDE, BISMUTH OXIDE, COBALT OXIDE, AND MANGANESE OXIDE.

1972 TAKESHI MASUYAMA ETAL 3,687,871

NONLINEAR RESISTOR AND NONLINEAR RESISTOR COMPOSITION Filed July 24, 1970 7Ms Tw mam/14 m nil/10 mafia 0440 ,b

75.74 yaw/ AJIs/H INVENTORS I 1 07"? 0 /5/1077 fir/m? United States Patent 3,687,871 NONLINEAR RESISTOR AND NONLINEAR RESISTOR COMPOSITION Takeshi Masuyama, Matsuoka Takatsuki, Hirakata Michio, and Tsuyoshi Nishi, Moriguchi, Japan, assignors to Matsushita Electric Industrial Co., Ltd., Kadoma, Osaka, Japan Filed July 24, 1970, Ser. No. 57,977 Int. Cl. H0lb 1/06 US. Cl. 252--518 12 Claims ABSTRACT OF THE DISCLOSURE A resistor composition having a nonlinear voltage characteristic consisting essentially of zinc oxide and, as an additive bismuth fluoride, and a nonlinear resistor made from said composition. The resistor composition and the resistor have the electrical properties thereof further improved by the addition of at least one member selected from the group consisting of cobalt fluoride, manganese fluoride, stannous fluoride, nickel fluoride, chromium fluoride, bismuth oxide, cobalt oxide, and manganese oxide.

This invention relates to resistor composition and re,- sistors having a nonlinear voltage characteristic, i.e. nonohmic resistance, due to the bulk thereof and more particularly to varistors comprising zinc oxide and bismuth fluoride.

Various nonlinear resistors such as silicon carbide varistors, selenium rectifiers and germanium or silicon p-n junction diodes, have been widely used for stabilization of voltage or current of electrical circuits. The electrical characteristics of such a nonlinear resistor are expressed by the relation:

Where V is the voltage across the resistor, I is the current flowing through the resistor, C is a constant corresponding to the voltage at a given current and exponent 7B is a numerical value greater than 1. The value of n is calculated by the following equation:

where V and V are the voltages at given currents I and I respectively. The desired value of C depends upon the kind of application to 'which the resistor is to be put. It is ordinarily desirable that the value of n be as large as possible since this exponent determines the extent to which the resistors depart from ohmic characteristics.

It is diflicult in varistors comprising germanium or silicon p-n junction diodes to control "the C-value over a wide range because the nonlinearity of these varistors is not attributable to the bulk but to the p-n junction. On the other hand, silicon carbide varistors have nonlinear characteristics due to the contacts among the individual grains of silicon carbide bonded together by a ceramic binding material, i.e. to the bulk, and the Cvalue is controlled by changing the dimension in the direction in which the current flows through the varistors. Silicon carbide varistors, however, have a relatively low n-value and are prepared by firing in a non-oxidizing atmosphere, especially for the purpose of obtaining a lower C-value. An object of the present invention is to provide a resistor having a nonlinear voltage characteristic due to the bulk thereof and characterized by a high n-value.

Another object of the invention is to provide a resistor composition from which such resistors can be made.

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T he details of the invention will become apparent upon consideration of the following description taken together with the accompanying drawing in which the single figure is a partly cross-sectional view through a resistor having a nonlinear voltage characteristic in accordance with the invention.

Before proceeding with a detailed description of the resistors and the resistor compositions contemplated by the invention, the resistor construction will be described with reference to the aforesaid figure of drawing wherein reference character 10 designates, as a whole, a nonlinear resistor comprising, as its active element, a sintered body having a pair of electrodes 2 and 3 applied to opposite surfaces thereof. Said sintered body 1 is prepared in a manner hereinafter set forth and can be in any form such as circular, square or rectangular plate form. Wire leads 5 and 6 are attached conductively to the electrodes 2 and 3, respectively, by a connection means 4 such as solder or the like.

A nonlinear resistor according to the invention comprises a sintered body of a batch composition consisting essentially of, as a major part, 99.95 to 9.0 mole percent of zinc oxide and, as an additive, 0.05 to 10.0 mole percent of bismuth fluoride. Such a nonlinear resistor has non-ohmic resistance due to the bulk itself. Therefore, its C-value can be changed without impairing the n-value by changing the distance between the opposite surfaces of a body thereof. A shorter distance results in a lower C-value.

A higher n-value can be obtained when said additive consists essentially of 0.3 to 2.5 mole percent of bismuth fluoride in accordance with the invention.

According to the present invention, the n-value can be further elevated when said additive further includes 0.05 to 10.0 mole percent of at least one member selected from the group consisting of cobalt fluoride, manganese fluoride, stannous fluoride, nickel fluoride and chromium fluoride. Superior results are obtained with an additive consisting essentially of 0.3 to 2.5 mole percent of bismuth fluoride and 0.1 to 3.0 mole percent of at least one member selected from the group consisting of cobalt fluoride, manganese fluoride, stannous fluoride, nickel fluoride, and chromium fluoride.

According to the present invention, the resistor has an extremely high n-value when said additive consists essentially of 0.3 to 2.5 mole percent of bismuth fluoride and 0.05 to 5.0 mole percent at least one member selected from the group consisting of cobalt oxide and manganese oxide.

Further, an extremely high n-value can be obtained when said additive consists essentialy of 0.3 to 2.5 mole percent of bismuth fluoride, 0.05 to 5.0 mole percent of cobalt oxide and 0.05 to 5.0 mole percent of at least one member selected from the group consisting of manganese fluoride and chromium fluoride.

The n-value is greatly elevated when said additive consists essentially of 0.3 to 2.5 mole percent of bismuth fluoide, 0.05 to 5.0 mole percent of manganese oxide and 0.05 to 5.0 mole percent of ot least one member selected from the group consisting of cobalt fluoride and chromium fluoride.

The sintered body 1 can be prepared by a per se well known ceramic technique. The starting materials in the compositions described in the foregoing description are mixed in a wet mill so as to produce homogeneous mixtures. The mixtures are dried and pressed in a mold into desired shapes at a pressure of from kg./cm to 1000 kg./cm. The pressed bodies are sintered in air at a temperature of l000 to 1400 C. for l to 3 hours, and then furnace-cooled to room temperature (about 15 to about 30 (-3.).

The mixtures can be preliminarily calcined at about 700 C. and pulverized for easy fabrication in the subsequent pressing step. The mixture to be pressed can be admixed with a suitable binder such as water, polyvinyl alcohol, etc.

It is advantageous that the opposite surfaces of the sintered body be lapped by abrasive powder such as silicon carbide having a particle size of 300 mesh to 1500 mesh.

The sintered bodies are provided, on the opposite surfaces thereof, with electrodes by any available and suitable method.

Lead wires can be attached to the electrodes in a per se conventional manner by using conventional solder having a low melting point. It is convenient to employ a conducsize of 10 mm. diameter and 1.5 mm. thickness. The opposite surfaces of the sintered disc are provided with a spray metallized film of aluminum by a per se well known technique. Lead wires are attached to the aluminum electrodes by means of conductive silver paint. The electrical characteristics of the resultant resistors are shown in Table 2. It will be readily understood that the n-value can be raised by the addition of at least one member selected from the group consisting of cobalt fluoride, manganese fluoride, stannous fluoride, nickel fluoride and chromium fluoride. For example, the addition of 0.3 mole percent of bismuth fluoride, 0.1 mole percent of cobalt fluoride and 0.1 mole percent of manganese fluoride results in a 60 volt C-value at 1 ma. and an rz-value of 14.

tive adhesive comprising silver powder and resin in an 5 organic solvent in order to connect the lead wires to the electrodes.

Nonlinear resistors according to this invention have a high stability with respect to temperature and in a load TABLE 2 life test, which is carried out at 70 C. at a rating power 20 1 Electrica for 500 hours. The It value and C value do not change Composition (mole percent) characten-stics very much after heating cycles and a load life test. It 1s v 5 G at advantageous for achievement of a high stab1l1ty w1th Bin Additive hm) n respect to humidity that the resultant nonlinear reslstors be embedded in a humidity proof resin such as epoxy resin 8: 8g 2g 23 8 or phenol resin in a per se well known manner. 10 00F. 0. 75 7. s Presently preferred illustrative embodiments of the g; invention are as follows: 0. 3 0013. 3. 0 50 14 O EXAMPLE 1 0.5 @052 0.5 45 20 0. 05 MnFz 0. 05 110 8.3 Starting materials listed in Table 1 are mixed in a wet 1 3 01 12 8% 2:7 mill for 5 hours. Mnz 10 9. g

0 a u o I I I l I The mixture 1s dried and pressed 1n a mold into a disc 72 of 13 mm. diameter and 2.5 mm. thickness at a ressure M111 0.1 71 1 f k 2 p 2. 5 Ml'lFz 3- 0 69 18 0 0.5 MnFz 0.5 55 The pressed body 1s sintered in air for 1 hour at a 8-82 E g: 3 23 g-g temperature of 1000 to 1400 C., and then furnace- 0.05 90 cooled to room temperature (about 15 to about C.). 1% girl? n; 2% 8. 2 The sintered disc has the opposite surfaces lapped by slli- 1 2 63 11 con carbide abrasive having a particle size of 600 mesh g-g l 2% %2 until it is to the thickness listed in Table 1. The opposite 5 5 5o 18 surfaces of the sintered disc are provided with a spray 1 M5 30 0. 05 N11 10 78 7.0 metallrzed film of aluminum by a per se well known tech- 10 77 g nique. Lead wires are attached to the aluminum electrodes g g by means of conductive silver paint. The electrical charac- 3 0 63 11 teristics of the resultant resistors are shown in Table 1. It gg3 will be readily understood that the C-value changes in 0.5 NiFz 0.5 17 proportion to the thickness of the sintered body. 8: 8g g 10 CrFa 0 05 123 0.4 TABLE 1 l0 OrFs 10 120 8.4 0.3 CIFa 0.1 85 11 Electrical 0.3 CrFa 3.0 73 12 Composition (mole percent) Thickcharacteristics 2.5 CrF 0.1 75 14 temp. ness 2.6 CrF 3.0 73 14 ZnO B11 0.) a. (ml-n.) 0 (at 1 ma.) 'n 0.5 CrF 0.5 18

0.3 1,200 1.0 30 4.4 0.5 1,200 1.0 20 5.0 1 1,200 1.0 41 4.8 2.5 1,200 1.0 50 4.0 13 $88 i8 52 2'5 0.5 11000 110 72 8:0 EXAMPLE 3 is t8 :2 21. 315 11308 1,0 2 4:4 Starting materials according to Table 3 are pressed, 8 fired, lapped and electrodes attached 1n the same manner 0.5 1,200 2.0 40 5.1 0.5 1,200 1.5 3 5,0 as descnbed 1n Example 2. The electrical characterlstlcs 8-2 i'ggg -g 2'8 of the resultant resistors are shown in Table 3. It can be easily understood that when the zinc oxide sintered body includin bismuth fluoride further includes cobalt oxide EXAMPLE 2 g or manganese oxide, and other fluorides such as listed in Table 3, the resultant sintered body has excellent nonlinear properties. Similar results can be obtained from the addition of bismuth fluoride, cobalt oxide and manganese oxide. For example, the addition of 0.5 mole percent of bismuth fluoride, 0.5 mole percent of cobalt oxide and 0.5 mole percent of manganese oxide results in an volt C-value at 1 ma. and an n-value of 25.

TABLE 3 Electrical Composition (mole percent) characteristics (at BiFi Additives 1 ma.) n

0.3 C00 0.05 95 16 0.5 000 0.5 60 23 2.5 C00 5.0 88 17 0.3 M110 0.05 263 19 0.5 MnO 0.5 125 26 2.5 MnO 5.0 240 18 0.3 C00 0.05 MnFz 0.05 112 20 0.5 000 0.5 MnFg 0.5 75 35 2.5 000 5.0 MnFg 5.0 105 21 0.3 000 0.05 CrF; 0.05 243 22 0.5 000 0.5 CrFa 0.5 120 30 2.5 000 5.0 CrFz 5.0 220 18 0.3 MnO 0.05 00F: 0.05 183 22 0.5 MnO 0.5 GoFz 0.5 62 34 2.5 MnO 5.0 00F: 5.0 200 21 0.3 MnO 0.05 OIFZ 0.05 304 18 0.5 MnO 0.5 CrFa 0.5 140 31 2.5 MnO 0 OrFa 5.0 295 19 EXAMPLE 4 and 0.05 to 5.0 mole percent of at least one member The resistors of Examples 1, 2 and 3, were tested in accordance with a method widely used in testing electronic components parts. The load life test was carried out at 70 C. ambient temperature at 1 watt rating power for 500 hours. The heating cycle test was carried out by repeating 5 times a cycle in which said resistors were kept at 85 C. ambient temperature for 30 minutes, cooled rapidly to 20 and then kept at such temperature for 30 minutes. Table 4 shows the average change rates of the C-value and the n-value of the resistors after the heating cycles and the load life test.

TABLE 4 selected from the group consisting of manganese fluoride and chromium fluoride.

7. A resistor as claimed in claim 1, wherein said additive consists essentially of 0.3 to 2.5 mole percent of bismuth fluoride, 0.05 to 5.0 mole percent of manganese oxide and 0.05 to 5.0 mole percent of at least one member selected from the group consisting of cobalt fluoride and chromium fluoride.

8. A resistor composition having a nonlinear voltage characteristics, said composition consisting essentially of, as a major part, 99.95 to 90.0 mole percent of zinc oxide,

Change rate after Change rate after life test heating cycle Composition (mole percent) (percent) test (percent) ZnO BiFs Additives Ac An Ac an 99.5. 0. 5 7. 4 6. 9 +3. 8 7. 9 99.0. 0. 5 00F: 0. 5 4. 3 4. 0 3. 0 6. 9 99.0. 0. 5 MnFz 0. 5 3. 9 3. 9 3. 6 5. 8 99.0- 0. 5 SnFz 0. 5 3. 0 2. 2 +2. 5 4. 0 99.0- 0. 5 NiFn 0. 5 2. 6 3. 5 +2. 4 3. 3 99.0. 0. 5 CrFa 0. 5 2. 8 3. 5 4. l. 3. 9 99.0. 0. 5 C00 0. 5 3. 3 4. 0 +1. 2 4. 4 99.0- 0. 5 MnO 0. 5 2. 9 2. 8 -1. 3 3. 3 98.5. 0. 5 C00 0. 5 +2. 0 2. 2 3. 4 2. 0 98.5. 0. 5 C00 0. 5 -1. 2 1. 2 +1. 0 1. 5 98.5. 0. 5 MnO 0. 5 1. 0 1. 2 +1. 0 -1. 5 98.5 0.5 M110 0.5 0.5 -1.0 l.2 0.9

What 1s clalmed 1s: and, as an add1t1ve, 0.05 to 10.0 mole percent of bismuth 1. A resistor having a nonlinear voltage characteristic comprising a sintered body having a composition consisting essentially of, as a major part, 99.95 to 90.0 mole percent of zinc oxide and, as an additive, 0.05 to 10.0 mole percent of bismuth fluoride which body has been sintered in air at 1000-1400" C. for from 1-3 hours.

2. A resistor as claimed in claim 1, wherein said additive further consists essentially of 0.05 to 10.0 mole percent of at least one member selected from the group consisting of cobalt fluoride, manganese fluoride, stannous fluoride, nickel fluoride and chromium fluoride.

3. A resistor as claimed in claim 1, wherein said additive consists essentially of 0.3 to 2.5 mole percent of hismuth fluoride.

4. A resistor as claimed in claim 3, wherein said additive further consists essentially of 0.1 to 3.0 mole percent of at least one member selected from the group consisting of cobalt fluoride, manganese fluoride, stannous fluoride, nickel fluoride and chromium fluoride.

5. A resistor as claimed in claim 1, wherein said additive consists essentially of 0.3 to 2.5 mole percent of bismuth fluoride and 0.05 to 5.0 mole percent of one member selected from the group consisting of cobalt oxide and manganese oxide.

6. A resistor as claimed in claim 1, wherein said additive consists essentially of 0.3 to 2.5 mole percent of bismuth fluoride, 0.05 to 5.0 mole percent of cobalt oxide fluoride, and said additive further consisting essentially of 0.05 to 10.0 mole percent of at least one member selected from the group consisting of cobalt fluoride, manganese fluoride, stannous fluoride, nickel fluoride and chromium fluoride.

9. A resistor composition having a nonlinear voltage characteristic, said composition consisting essentially of, as a major part, 99.95 to 90.0 mole percent of zinc oxide and, as an additive, 0.3 to 2.5 mole percent of bismuth fluoride, and said additive further consisting essentially of 0.1 to 3.0 mole percent of at least one member selected from the group consisting of cobalt fluoride, manganese fluoride, stannous fluoride, nickel fluoride and chromium fluoride.

10. A resistor composition having a nonlinear voltage characteristic, said comopsition consisting essentially of, as a major part, 99.95 to 90.0 mole percent of zinc oxide, and, as an additive 0.3 to 2.5 mole percent of bismuth fluoride, and said additive further consists essentially of 0.05 to 5.0 mole percent of one member selected from the group consisting of cobalt oxide and manganese oxide.

11. A resistor composition having a nonlinear voltage characteristic, said composition consisting essentially of, as a major part, 99.95 to 90.0 mole percent of zinc oxide, and, as an additive, 0.3 to 2.5 mole percent of bismuth fluoride, and said additive further consists essentially of 8 0.05 to 5 .0 mole percent of cobalt oxide and 0.05 to 5.0 5.0 mole percent of at least one member selected from the mole percent of at least one member selected from the group consisting of cobalt fluoride and chromium fluoride. group consisting of manganese fluoride and chromium fl id References Cited 12. A resistor composition having a nonlinear voltage 5 UNITED STATES PATENTS characteristic, said composition consisting essentially of, 3,089,356 5/1963 Cyr et a] 52 51g as a major part, 99.95 to 90.0 mole percent of zinc oxide 3,551,35 12 1970 Bowman 252 52() and, as an additive, 0.3 to 2.5 mole percent of bismuth 3,503 029 3 197 Matsuoka 252.418

fluoride, and said additive further consists essentially of 0.05 to 5.0 mole percent of manganese oxide and 0.05 to 10 DOUGLAS S. DRUMMOND, Primary Examiner 

